Apparatus and Method for Selective Single-Carrier Equalization

ABSTRACT

Embodiments of an apparatus and method for selective SC equalization are provided. Multipath propagation in a communication channel often changes, and the severity of multipath propagation is often below worst case conditions supported by a SC communication device. When multipath propagation is less severe and below worst conditions, the use of FDE in a SC receiver to mitigate ISI can be overkill and can result in excess power being consumed. The excess power consumption can be attributed to the general inability of the structure used to perform FDE to scale in terms of performance with channel conditions. Embodiments of the apparatus and method for performing selective equalization in a SC receiver allow either FDE or TDE to be performed based on the current multipath propagation conditions of a communication channel. In general, TDE is used in place of FDE to conserve power when channel conditions permit.

FIELD OF THE INVENTION

This application relates generally to channel equalization for receiversand more particularly to selective channel equalization forsingle-carrier receivers.

BACKGROUND

Communication systems are designed to transfer information between twodevices over a channel in the presence of disturbing influences.Intersymbol interference (ISI) is one well-known disturbing influence inwhich transmitted symbols become elongated and interfere with adjacentlytransmitted symbols. This spreading or “smearing” of symbols isgenerally caused by multipath propagation within those channels. BecauseISI has the same effect as noise, communication is made less reliable.

One of the most basic solutions for mitigating the effects of ISI isslowing down the speed at which symbols are transmitted over a channel.More specifically, the transmission speed can be slowed down such that asymbol is only transmitted after allowing previously transmitted symbolpulses to dissipate. The time it takes for a transmitted symbol pulse todissipate is called delay spread, whereas the original time of thesymbol pulse (including any time before the next symbol pulse istransmitted) is called the symbol time. No ISI will occur if the delayspread is less than or equal to the symbol time. Although slowing downthe symbol rate can eliminate or reduce the effects of ISI, it isgenerally an unacceptable solution for many of today's bandwidthintensive communication applications, such as those involving thetransfer of multimedia content.

Orthogonal frequency division multiplexing (OFDM) is a multicarriercommunication scheme that builds on this basic solution of slowing downthe symbol rate to mitigate ISI. In an OFDM communication system, aplurality of orthogonal sub-carriers are transmitted over a singlechannel at the same time. The symbol rate of the communication systemcan be divided among the sub-carriers, allowing the symbol time to beincreased and, thus, the effects of ISI to be reduced and more easilycompensated for using equalization. Although OFDM provides a goodsolution for ISI mitigation, it suffers from several drawbacks,including a high peak-to-average power ratio (PAPR), which limits theefficiency of power amplifiers used in OFDM communication devices.

An alternative to OFDM that does not suffer from a high PAPR issingle-carrier (SC) modulation combined with frequency-domainequalization (FDE). A SC communication device transmits and receives aSC modulated by symbols that each convey one or more bits ofinformation. FDE is a filtering process that is used to flatten thefrequency response of the channel over which the SC is transmitted tomitigate the effects of ISI. In general, FDE is performed on a block ofsymbols received via the SC and involves a fast Fourier transform (FFT)of the block of symbols and a channel inversion operation. Morespecifically, the FFT converts a time domain block of symbols receivedvia the SC into a frequency domain signal, which is then equalized bymultiplying it point-by-point by an estimate of the inverse frequencyresponse of the channel. SC modulation combined with FDE is an effectivetechnique for reducing the effects of ISI and delivers performance inline with OFDM, even for channels with long delay spread (i.e., channelswith long impulse responses).

However, one drawback of SC communication devices that use FDE tomitigate ISI is that the structure used to perform FDE generally doesnot scale in terms of performance with changing channel conditions. As aresult, FDE is generally always performed under the assumption of worstcase channel conditions. Because multipath propagation of a channeloften changes and is often below worst case conditions, FDE is oftenperformed in SC communication devices at a level beyond what is requiredat the cost of excess power being consumed. For example, at any givenpoint in time the multipath conditions of a channel may not be severeand may result in a short delay spread. Under these conditions, a SCcommunication device receiving information over the channel and usingFDE to mitigate ISI may be performing and consuming power beyond what isrequired to properly recover the information. Since power consumption isoften critical in SC communication devices that may be dependent onbatteries, for example, any excess power consumed decreases the utilityof these devices.

Another drawback of SC communication devices that use FDE to mitigateISI is that the structure used to perform FDE generally does not scalein terms of performance with the signal-to-noise ratio (SNR) requirementof the receiver (i.e. with the SNR required or desired for properlyrecovering information modulated onto a SC), which is often dynamic. Forexample, the SNR requirement of the receiver can change based on theconstellation order of the digital modulation scheme used to modulatethe SC. If an SC communication device that uses FDE to mitigate ISI iscurrently receiving a SC modulated in accordance with a digitalmodulation scheme having a relatively low-order constellation (e.g.,BPSK or QPSK), FDE likely will be performed in the SC communicationdevice at a level beyond what is required at the cost of excess powerbeing consumed.

Therefore, what is needed is an apparatus and method for reducing thepower consumption of a SC communication device that uses FDE whenmultipath propagation conditions of the channel permit or when thedynamic SNR requirement of the SC communication device permits.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1 illustrates a SC receiver with selective equalization, accordingto embodiments of the present invention.

FIG. 2 illustrates a frequency-domain equalizer, according toembodiments of the present invention.

FIG. 3 illustrates a time-domain equalizer, according to embodiments ofthe present invention.

FIG. 4 illustrates an equalization selector, according to embodiments ofthe present invention.

FIG. 5 illustrates a flowchart of a method for performing selectiveequalization on a single-carrier (SC) received over a multipathpropagation channel, according to embodiments of the present invention.

The present invention will be described with reference to theaccompanying drawings. The drawing in which an element first appears istypically indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the invention. However, itwill be apparent to those skilled in the art that the invention,including structures, systems, and methods, may be practiced withoutthese specific details. The description and representation herein arethe common means used by those experienced or skilled in the art to mosteffectively convey the substance of their work to others skilled in theart. In other instances, well-known methods, procedures, components, andcircuitry have not been described in detail to avoid unnecessarilyobscuring aspects of the invention.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

Overview

As discussed above, multipath propagation in a communication channeloften changes, and the severity of multipath propagation is often belowworst case conditions supported by a SC communication device. Whenmultipath propagation is less severe and below worst case conditions,the use of FDE in a SC receiver to mitigate ISI can be overkill and canresult in excess power being consumed. The excess power consumption canbe attributed to the general inability of the structure used to performFDE to scale in terms of performance with channel conditions. Describedbelow is an apparatus and method for performing selective equalizationin a SC receiver that allows either FDE or time-domain equalization(TDE) to be performed based on the current multipath propagationconditions of a communication charnel (or based on the dynamic SNRrequirement of the SC communication device). In general, TDE can be usedin place of FDE to conserve power when channel conditions permit.

Exemplary SC Receiver with Selective Equalization

FIG. 1 illustrates a SC receiver 100 configured to selectively performeither FDE or TDE, according to embodiments of the present invention. SCreceiver 100 can be used within several different devices, includingmobile phones, personal digital assistants, laptops, set-top boxes, androuters, to name a few. As illustrated in FIG. 1, SC receiver 100includes an antenna 105, a front end 110, an analog-to-digital converter(ADC) 115, a hybrid frequency-domain/time-domain equalizer 120, ademapper 125, and an equalization selector 130.

In operation, antenna 105 is configured to receive a SC modulated withinformation, such as video, audio, and data, over a multipathpropagation channel. Front end 110 performs down-conversion andfiltering of the received SC and outputs a baseband signal. The basebandsignal is then converted to a digital signal comprising a series ofunequalized symbols that each convey one or more bits of information. Inanother embodiment of SC receiver 100, ADC 115 is positioned prior tofront end 110 and down conversion and filtering are performed in thedigital domain.

After being provided by ADC 115, the unequalized symbols are processedby hybrid frequency-domain/time-domain equalizer 120 to mitigate ISIcaused by multipath propagation of the channel. Hybridfrequency-domain/time-domain equalizer 120 includes hardware configuredto perform either FDE or TDE on the symbols. More specifically, hybridfrequency-domain/time-domain equalizer 125 is configured to performeither FDE using frequency-domain equalizer 135 or TDE using time-domainequalizer 140 at any given point in time based on an equalization typeselection signal generated by equalization selector 130.

Time-domain equalizer 140 is specifically configured to perform ISImitigation using a filter (not shown), such as a transversal filter. Inorder to effectively mitigate ISI, the number of taps of the filter isusually required to be on the order of the number of data symbolsspanned by the delay spread of the communication channel. Therefore, fora channel with a current delay spread that is large, the complexity andpower consumption of time-domain equalizer 140 can become exorbitant. Inthese instances, when multipath propagation is severe and delay spreadis large, frequency-domain equalizer 135 can be utilized to reducecomplexity and save power. However, for a channel that currently has asmall delay spread, time-domain equalizer 140 can be utilized with lesscomplexity and power consumption than frequency-domain equalizer 135.

If fact, the filter of time-domain equalizer 140 can be made to have aprogrammable number of filter taps such that the filter can beprogrammed to use a custom number of filter taps based on a currentestimate of the delay spread. For example, the filter of time-domainequalizer 140 can be programmed to use less filter taps when there isless delay spread and more filter taps when there is more delay spread.In this way, additional power can be conserved because signals going tounused filters taps can be gated (e.g., any clock signal going to theunused filter taps can be gated) to reduce dynamic power consumption.

In one embodiment, equalization selector 130 is configured to receiveand process the unequalized symbols from ADC 115 to generate an estimateof the delay spread of the communication channel. If the number of datasymbols spanned by the delay spread of the channel is above a certainthreshold, equalization selector 130 can signal to hybridfrequency-domain/time-domain equalizer 120, via the equalization typeselection signal, to perform FDE using frequency-domain equalizer 135.If, on the other hand, the number of data symbols spanned by the delayspread of the communication channel is below the threshold, equalizationselector 130 can signal to hybrid frequency-domain/time-domain equalizer120, via the equalization type selection signal, to perform TDE usingtime-domain equalizer 140. The threshold can be determined based on whenthe power consumption of time-domain equalizer 140 becomes greater thanthe power consumption of frequency-domain equalizer 135 for a givennumber of data symbols spanned by the delay spread.

In another embodiment, equalization selector 130 is configured toreceive and process information related to beamforming performed by SCreceiver 100 and/or the transmitter transmitting the SC. In general,beamforming can be used to effectively reduce the delay spread of thechannel. Therefore, based on the availability and degree of beamformingperformed by SC receiver 100 and/or the transmitter transmitting the SC,equalization selector 130 can signal to hybridfrequency-domain/time-domain equalizer 120, via the equalization typeselection signal, to perform FDE using frequency-domain equalizer 135 orTDE using time-domain equalizer 140. More specifically, in the presenceof good beamforming, equalization selector 130 can signal to hybridfrequency-domain/time-domain equalizer 120, via the equalization typeselection signal, to perform TDE using time-domain equalizer 140 toconserve power, and in other instances, to perform FDE usingfrequency-domain equalizer 135.

In yet another embodiment, equalization selector 130 is configured toreceive and process the unequalized symbols from ADC 115 to generate anestimate of the frequency response and/or impulse response of thecommunication channel. For example, equalization selector 130 canestimate the frequency and/or impulse response of the channel over whichthe SC is received using a channel estimation method. The channelestimation method can be a training-based method or a blind method andcan use either maximum likelihood estimation or minimum mean squareerror estimation, for example. This estimated response of the channelincludes information related to (and is therefore dependent on) thedelay spread of the communication channel and can be used to determinean estimate of the signal-to-noise ratio (SNR) of the SC received by SCreceiver 100 after having being processed by frequency-domain equalizer135 or time-domain equalizer 140. This estimated SNR can be referred toas an effective SNR of the received SC for a given channel estimatedetermined and equalization scheme performed.

For example, equalization selector 130 can determine the effective SNRof a SC received by receiver 100, for a given channel estimate, afterhaving been processed by time-domain equalizer 140. In fact,equalization selector 130 can perform the same estimation for severaldifferent configurations of time-domain equalizer 140, each with adifferent number of taps being used by the filter performing TDE.Equalization selector 130 can further determine the effective SNR of theSC, for the same channel estimate, after having been processed byfrequency-domain equalizer 135. These estimates can then be used todetermine whether time-domain equalizer 140 is sufficient to process areceived SC or whether frequency-domain equalizer 135 is required.

More specifically, given a required SNR that represents a required ordesired SNR for properly recovering information modulated onto a SCreceived by SC receiver 100, a comparison can be made between therequired SNR and the effective SNR of the SC after being processed bytime-domain equalizer 140. If the effective SNR of the SC after beingprocessed by time-domain equalizer 140 is expected to be greater thanthe required SNR, time-domain equalizer 140 can be used to performequalization. If, on the other hand, the effective SNR of the SC afterbeing processed by time-domain equalizer 140 is expected to be less thanthe required SNR, frequency-domain equalizer 135 can be used in place oftime-domain equalizer 140.

In an embodiment, equalization selector 130 can be further configured tocalculate the required SNR based on one or more conditions. For example,equalization selector 130 can determine the required SNR based on theconstellation order of the digital modulation scheme used to modulatethe SC. In general, the higher the order constellation used in thedigital modulation of a carrier, such as the SC received by SC receiver100, the higher the required SNR imposed at the receiver in order toreliably demodulate the carrier-signal and recover the transmittedinformation. Thus, the required SNR can be determined to be greater fordigital modulation schemes with higher order constellations than fordigital modulation schemes with lower order constellations.

In another example, equalization selector 130 can determine the requiredSNR based on the type of information modulated onto the SC. For example,certain types of information such as video, audio, and data may be ableto tolerate different amounts of lost or corrupted information ordifferent amounts of delay in receiving the information transmitted overthe channel. These differences can dictate different levels of requiredSNR for each of the different types of information modulated onto theSC.

In yet another example, equalization selector 130 can determine therequired SNR based on a code rate used to encode the informationmodulated onto the SC. More specifically, prior to transmission, atransmitter can add redundant information to the information modulatedonto the SC. The redundant information is typically a complex functionof a portion, or group, of the original information bits, and allows forforward error correction (FEC) to be performed at a receiving system,such as SC receiver 100. FEC enables a receiving system to detect andcorrect for errors caused by corruption from the channel and receiver.The total amount of useful information sent, i.e. non-redundantinformation, is typically defined by the code rate, k/n; for every kbits of useful information, n bits of information are generated.Consequently, increasing the code rate invariably increases the datarate. However, a higher code rate imposes a higher SNR requirement atthe receiver in order to reliable demodulate received signals. Thus,equalization selector 130 can determine the required SNR, at least inpart, based on the code rate used to encode the information modulatedonto the SC.

In a final example, equalization selector 130 can determine the requiredSNR based on information related to beamforming performed by SC receiver100 and/or the transmitter transmitting the SC. For example, theinformation related to beamforming can be in the form of a gain realizedby performing beamforming compared to omnidirectional reception ortransmission.

It should be further noted that equalization selector 130 can furtheradd an additional SNR margin to any required SNR determined to betterensure proper recovery of information modulated onto the SC received bySC receiver 100.

After equalization selector 130 determines which form of equalization isto be performed, the unequalized symbols can be equalized by hybridfrequency-domain/time-domain 120. The equalized symbols produced byhybrid frequency-domain/time-domain 120 can then be provided to demapper125. Demapper 125, in the case of complex symbols, uses the phase andmagnitude information of each symbol and makes a decision as to whichcombination of one or more bits the transmitter sent based on thedigital modulation scheme used by the transmitter (e.g., 64-QAM,256-QAM, etc.). Demapper 125 can perform either hard decision decodingor soft decision decoding.

Exemplary Frequency-Domain Equalizer

FIG. 2 illustrates an exemplary frequency-domain equalizer 200 that canbe implemented in SC receiver 100 illustrated in FIG. 1, according toembodiments of the present invention. As illustrated in FIG. 2,frequency-domain equalizer 200 includes a cyclic prefix (CP) remover205, a serial-to-parallel module 210, an N-point FFT 215, a complexmultiplier bank 220, an N-point IFFT 225, and a parallel-to-serialmodule 230.

In operation, frequency-domain equalizer 200 is configured to performFDE on a group of noisy symbols that were recovered from a SCtransmitted over a multipath propagation channel. For each group ofnoisy symbols, cyclic prefix samples are removed by CP remover 205 andthe resulting group of symbols is sent to serial-to-parallel module 210.Serial-to-parallel module 210 converts the block of symbols intoN-parallel symbols for processing by N-point FFT 215. N-point FFT 215converts the finite duration sequence of N symbols into an N-pointfrequency-domain signal, where each point of the N-pointfrequency-domain signal represents a specific frequency component of thefinite duration sequence of N symbols. The integer value N is usuallychosen in the range of 64-2048 for SC communication systems. The N-pointfrequency-domain signal is then sent to complex multiplier bank 220 forfurther processing.

A more detailed example implementation 235 of complex multiplier bank220 is provided in the bottom right hand corner of FIG. 2. Eachfrequency component of the N-point frequency-domain signal (denoted byIN₀-IN_(N-1)) is multiplied by a coefficient (denoted by C₀-C_(N-1)).The resulting output (denoted by OUT₀-OUT_(N-1)) represents theequalized N-point frequency-domain signal. The coefficient values aredetermined so as to flatten the frequency response of the multipathpropagation channel. More specifically, each coefficient value isgenerally determined solely as a function of the channel frequencyresponse at the corresponding frequency of the coefficient. Because eachcoefficient is generally determined solely as a function of the channelfrequency response, the complexity of frequency-domain equalizer 200generally does not scale with the delay spread of the channel.

After channel distortion has been compensated for by multiplier bank220, the N-point frequency-domain signal is brought back into thetime-domain by N-point IFFT 225. The parallel, time-domain signal of Nsymbols produced by N-point IFFT 225 is then re-serialized byparallel-to-serial module 230.

Exemplary Time-Domain Equalizer

FIG. 3 illustrates an exemplary time-domain equalizer 300 that can beimplemented in SC receiver 100 illustrated in FIG. 1, according toembodiments of the present invention. As illustrated in FIG. 3,time-domain equalizer 300 is implemented as an finite impulse response(FIR), transversal filter that includes one or more continuous-timedelay elements denoted by the symbol D and one or more taps (i.e.,multipliers). The delay elements are cascaded to store and shift, forexample, successive noisy symbols that were recovered from a SCtransmitted over a multipath propagation channel.

Time-domain equalizer 300 can include as few as one delay element andtap or up to N delay elements and taps. In one embodiment, the number oftaps used by time-domain equalizer 300 to perform time-domainequalization is programmable. If fact, the filter of time-domainequalizer 300 can be made to have a programmable number of taps suchthat the filter can be programmed to use a custom number of taps basedon the current delay spread of the multipath propagation channel. Forexample, the filter of time-domain equalizer 300 can be programmed touse less filter taps when there is less delay spread and more taps whenthere is more delay spread. In this way, additional power can beconserved because signals going to unused taps can be gated (e.g., anyclock signal going to the unused taps can be gated) to reduce dynamicpower consumption.

The filter of time-domain equalizer 300 can be used in a number ofdifferent time-domain equalizer configurations, including a feed-forwardequalizer (FFE) configuration and a decision feedback equalizer (DFE)configuration as will be recognized by one of ordinary skill in the art.For example, in a FFE configuration, a current symbol being processed bythe filter of time-domain equalizer 300 is stored in the last delayelement in the chain of delay elements, whereas future symbols (i.e.,symbols transmitted and received after the current symbol) are stored inthe remaining delay elements. The future symbols stored in the delayelements and just received are multiplied by respective tap weightsC₀-C_(N-2). The tap weights are related to the extent of precursor ISIcontributed by the future symbols. For example, tap weight C₁ representsa good approximation of the amount of precursor ISI contributed by thefuture symbol stored in the first delay element illustrated farthest tothe left in FIG. 3.

The resulting products of the multipliers are subtracted from thecurrent symbol being processed to substantially eliminate precursor ISIfrom that symbol. The current symbol, as illustrated in FIG. 3, can befurther multiplied by a tap weight C_(N-1). The tap weights can bedetermined by an adaptation engine (not shown) and can be continuallyadapted by the adaptation engine to change with the conditions of thechannel over which the information is received.

Exemplary Equalization Selector

FIG. 4 illustrates an equalization selector 400 that can be implementedin SC receiver 100 illustrated in FIG. 1, according to embodiments ofthe present invention. Equalization selector 400 represents oneembodiment of equalization selector 130 illustrated in FIG. 1. Asillustrated in FIG. 4, equalization selector 400 includes a channelestimator 405, an effective SNR calculator 410, a required SNRcalculator 415, and a comparator 420.

In operation, channel estimator 405 is configured to receive and processunequalized symbols that were recovered from a SC transmitted over amultipath propagation channel to generate an estimate of the frequencyresponse and/or impulse response of the channel. For example, channelestimator 405 can estimate the frequency and/or impulse response of thechannel over which the SC is received using a channel estimation method.The channel estimation method can be a training-based method or a blindmethod and can use either maximum likelihood estimation or minimum meansquare error estimation, for example.

This estimated response of the channel includes information related tothe delay spread of the communication channel and is used by effectiveSNR calculator 410 to determine an estimate of the signal-to-noise ratio(SNR) of the SC after having being processed by frequency-domainequalizer 135 or time-domain equalizer 140, as illustrated in FIG. 1.This estimated SNR can be referred to as an effective SNR of thereceived SC for a given channel estimate determined and equalizationscheme performed.

For example, effective SNR calculator 410 can determine the effectiveSNR of a SC received, for a given channel estimate, after having beenprocessed by time-domain equalizer 140. In fact, equalization selector130 can perform the same estimation for several different configurationsof time-domain equalizer 140, each with a different number of taps beingused by the filter performing TDE. SNR calculator 140 can furtherdetermine the effective SNR of the SC, for the same channel estimate,after having been processed by frequency-domain equalizer 135.

These estimates can then be used by comparator 420 to determine whethertime-domain equalizer 140 is sufficient to process a received SC orwhether frequency-domain equalizer 135 is required. More specifically,given a required SNR that represents a required or desired SNR forproperly recovering information modulated onto a SC received, comparator420 can compare the required SNR and the effective SNR of the SC afterbeing processed by time-domain equalizer 140. If the effective SNR ofthe SC after being processed by time-domain equalizer 140 is expected tobe greater than the required SNR, time-domain equalizer 140 (with agiven number of taps) can be used to perform equalization. If, on theother hand, the effective SNR of the SC after being processed bytime-domain equalizer 140 is expected to be less than the required SNR,frequency-domain equalizer 135 can be used in place of time-domainequalize 140 (or time-domain equalizer 140 with more taps being used toperform TDE).

Required SNR calculator 415 is configured to calculate the required SNRbased or one or more conditions. For example, required SNR calculatorcan determine the required SNR based on the constellation order of thedigital modulation scheme used to modulate the SC received. In general,the higher the order constellation used in the digital modulation of acarrier, such as the SC received, the higher the required SNR imposed atthe receiver in order to reliably demodulate the carrier-signal andrecover the transmitted information. Thus, the required SNR can bedetermined to be greater for digital modulation schemes with higherorder constellations than for digital modulation schemes with lowerorder constellations.

In another example, required SNR calculator 415 can determine therequired SNR based on the type of information modulated onto the SCreceived. For example, certain types of information such as video,audio, and data may be able to tolerate different amounts of lost orcorrupted information or different amounts of delay in receiving theinformation transmitted over the channel. These differences can dictatedifferent levels of required SNR for each of the different types ofinformation modulated onto the SC.

In yet another example, required SNR calculator 415 can determine therequired SNR based on a code rate used to encode the informationmodulated onto the SC received. More specifically, prior totransmission, a transmitter can add redundant information to theinformation modulated onto the SC received. The redundant information istypically a complex function of a portion, or group, of the originalinformation bits, and allows for forward error correction (FEC) to beperformed at a receiving system, such as SC receiver 100 illustrated inFIG. 1. FEC enables a receiving system to detect and correct for errorscaused by corruption from the channel and receiver. The total amount ofuseful information sent, i.e. non-redundant information, is typicallydefined by the code rate, k/n; for every k bits of useful information, nbits of information are generated. Consequently, increasing the coderate invariably increases the data rate. However, a higher code rateimposes a higher SNR requirement at the receiver in order to reliabledemodulate received signals. Thus, required SNR calculator 415 candetermine the required SNR, at least in part, based on the code rateused to encode the information modulated onto the SC.

In a final example, required SNR calculator 415 can determine therequired SNR based on information related to beamforming performed bythe SC receiver receiving the SC and/or the transmitter transmitting theSC. For example, the information related to beamforming can be in theform of a gain realized by performing beamforming compared toomnidirectional reception or transmission.

It should be further noted that required SNR calculator 415 can furtheradd an additional SNR margin to any required SNR determined to betterensure proper recovery of information modulated onto the SC received.

Exemplary Method for Performing Selective Equalization

FIG. 5 illustrates a flowchart 500 of a method for performing selectiveequalization on a single-carrier (SC) received over a multipathpropagation channel, according to embodiments of the present invention.Flowchart 500 is described with continued reference to the exemplary SCreceiver 100 depicted in FIG. 1. However, flowchart 500 is not limitedto that embodiment. Note that some steps in flowchart 500 do not have tooccur in the order shown or discussed below.

Flowchart 500 starts at step 505 and transitions to step 510. In step510, an effective SNR of the SC after having undergone TDE bytime-domain equalizer 140 is determined. This determination can beperformed for several different configurations of time-domain equalizer140, each with a different number of taps being used by the filterperforming TDE.

After step 510, the effective SNR(s) determined in step 510 are comparedto a required SNR. The required SNR can be determined according anynumber of conditions as discussed above. If the effective SNR is greaterthan the required SNR, flowchart 500 proceeds to step 520. Else,flowchart 500 proceeds to step 525.

In one embodiment, for multiple different effective SNRs determined instep 510, each of which corresponds to a different configuration oftime-domain equalizer 140 using a different number of taps, thedifferent effective SNRs determined can be compared in step 515 startingwith the effective SNR corresponding to the configuration of time-domainequalizer 140 using the least number of taps and working up to theeffective SNR corresponding to the configuration of time-domainequalizer 140 using the most number of taps to perform TDE. Once aneffective SNR is determined to be greater than the required SNR in step515, flowchart 500 can transition without making any additionalcomparisons. However, if after having going through each determined SNRcalculated in step 510 and comparing them with the required SNR and noneof the determined SNRs are greater than the required SNR, flowchart 500transitions to step 525.

Assuming a determined effective SNR is greater than the required SNR,flowchart 500 transitions to step 520 and time-domain equalization isperformed on the SC.

Assuming, on the other hand, that no determined effective SNR is greaterthan the required SNR, flowchart 500 transitions to step 525 and FDE isperformed on the SC. It should be noted that, in another embodiment, aneffective SNR can be determined for the SC after having undergone FDE todetermine whether FDE is sufficient (i.e., that the effective SNR of theSC after having undergone FDE is greater than the required SNR) prior tostep 520. If not, then the SC receiver can be shut down to conservepower. Else, FDE can be performed on the SC.

After steps 520 and 525, flowchart 500 returns to step 505 and themethod depicted can be repeated.

It should be noted that, although the detailed description abovegenerally described FDE and TDE based on feed-forward implementations,the present invention is not so limited. As will be appreciated by oneof ordinary skill in the art, the present invention can be applied toFDE and TDE based on feed-back implementation as well.

It should be further noted that, although the detailed description abovedescribed performing equalization using either FDE or TDE, the conceptspresented above can be applied more generally, as will be appreciated byone of ordinary skill in the art, to other equalization methods. Forexample, it is possible to apply the concepts above to select betweendifferent equalization methods, such as equalization methods EQ1, EQ2,and EQ3 where: EQ1, EQ2, and EQ3 can each represent any reasonableequalization method; EQ1 can consume power P1 and can be used for arequired SNR1, EQ2 can consume power P2 and can be used for a requiredSNR2, and EQ3 can consume power P3 and can be used for a required SNR3.The values of SNR1, 2, and 3 can be such that SNR1<SNR2<SNR3, and thevalues of P1, 2, and 3 can be such that P1<P2<P3. Therefore, and inaccordance with the above described concepts, depending on the requiredSNR and power consumption constraints, one of the equalization methodsEQ1, EQ1, and EQ3 can be selected.

Conclusion

It will be appreciated that the above described embodiments of theinvention may be implemented in hardware, firmware, software, or anycombination thereof. Embodiments of the invention may also beimplemented as instructions stored on a machine-readable medium, whichmay be read and executed by one or more processors. A machine-readablemedium may include any mechanism for storing or transmitting informationin a form readable by a machine (e.g., a computing device). For example,a machine-readable medium may include read only memory (ROM); randomaccess memory (RAM); magnetic disk storage media; optical storage media;flash memory devices; electrical, optical, acoustical or other forms ofpropagated signals.

It is to be appreciated that the Detailed Description section, and notthe Abstract section, is intended to be used to interpret the claims.The Abstract section may set forth one or more but not all exemplaryembodiments of the present invention as contemplated by the inventor(s),and thus, is not intended to limit the present invention and theappended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

1. A receiver for performing selective equalization on a single-carrier(SC) received over a multipath propagation channel, the receivercomprising: a frequency-domain equalizer configured to performfrequency-domain equalization (FDE) on the SC to compensate for noiseintroduced by the multipath propagation channel; a time-domain equalizerconfigured to perform time-domain equalization (TDE) on the SC tocompensate for noise introduced by the multipath propagation channel;and an equalization selector configured to select, based on an amount ofdelay spread associated with the multipath propagation channel, thefrequency-domain equalizer to perform FDE on the SC or the time-domainequalizer to perform TDE on the SC.
 2. The receiver of claim 1, whereinthe equalization selector is configured to select the frequency-domainequalizer to perform FDE on the SC or the time-domain equalizer toperform TDE on the SC based on information relating to beamformingperformed by the receiver or a transmitter transmitting the SC.
 3. Thereceiver of claim 1, wherein the equalization selector is configured toselect the time-domain equalizer to perform TDE on the SC if aneffective signal to noise ratio (SNR) of the SC after being processed bythe time-domain equalizer is expected to be greater than a required SNR,wherein the effective SNR is dependent on the amount of delay spreadassociated with the multipath propagation channel.
 4. The receiver ofclaim 3, wherein the equalization selector is configured to select thefrequency-domain equalizer to perform FDE on the SC if the effective SNRof the SC after having undergone TDE by the TDE is expected to be lessthan the required SNR.
 5. The receiver of claim 4, wherein the requiredSNR is determined based on a modulation order of a modulation schemeused to modulate the SC.
 6. The receiver of claim 4, wherein therequired SNR is determined based on a type of information modulated ontothe SC, wherein the type of information is at least one of video anddata.
 7. The receiver of claim 4, wherein the required SNR is determinedbased on a code rate used to encode information modulated onto the SC 8.The receiver of claim 4, wherein the required SNR is determined based oninformation relating to beamforming performed by the receiver or atransmitter transmitting the SC.
 9. The receiver of claim 3, wherein theeffective SNR is further dependent on a number of filter taps used bythe time-domain equalizer to perform TDE on the SC.
 10. The receiver ofclaim 9, wherein, if the equalization selector selects the time-domainequalizer to perform TDE on the SC, the equalization selector furtherprograms the time-domain equalizer to use a least number of filter tapsto perform TDE on the SC that still provides for an effective SNRgreater than the required SNR.
 11. A method for performing selectiveequalization on a single-carrier (SC) received over a multipathpropagation channel, the method comprising: performing time-domainequalization on the SC if an effective signal to noise ratio (SNR) ofthe SC after having undergone time-domain equalization (TDE) is expectedto be greater than a required SNR, wherein the effective SNR isdependent on the amount of delay spread associated with the multipathpropagation channel; and performing frequency-domain equalization on theSC if the effective SNR of the SC after having undergone TDE by thetime-domain equalizer is expected to be less than the required SNR. 12.The method of claim 11, further comprising: determining the required SNRbased on a modulation order of a modulation scheme used to modulate theSC.
 13. The method of claim 11, further comprising: determining therequired SNR based on a type of information modulated onto the SC,wherein the type of information is at least one of video and data. 14.The method of claim 11, further comprising: determining the required SNRbased on a code rate used to encode information modulated onto the SC15. The method of claim 11, further comprising: determining the requiredSNR based on information relating to beamforming performed by a receiverreceiving the SC or a transmitter transmitting the SC.
 16. The method ofclaim 11, wherein the effective SNR is further dependent on a number offilter taps used by the time-domain equalizer to perform TDE on the SC.17. The method of claim 16, further comprising: if the effective SNR ofthe SC after having undergone TDE is expected to be greater than therequired SNR, using a least number of filter taps to perform TDE on theSC that still provides for an effective SNR greater than the requiredSNR.
 18. A receiver for performing selective equalization on asingle-carrier (SC) received over a multipath propagation channel, thereceiver comprising: a frequency-domain equalizer configured to performfrequency-domain equalization (FDE) on the SC to compensate for noiseintroduced by the multipath propagation channel; a time-domain equalizerconfigured to perform time-domain equalization (TDE) on the SC tocompensate for noise introduced by the multipath propagation channel,wherein the time-domain equalizer uses a programmable number of filtertaps to perform TDE on the SC; and an equalization selector configuredto select, based on an amount of delay spread associated with themultipath propagation channel, the frequency-domain equalizer to performFDE on the SC or the time-domain equalizer to perform TDE on the SC. 19.The receiver of claim 18, wherein the equalization selector isconfigured to select the time-domain equalizer to perform TDE on the SCif an effective signal to noise ratio (SNR) of the SC after beingprocessed by the time-domain equalizer is expected to be greater than arequired SNR, wherein the effective SNR is dependent on the amount ofdelay spread associated with the multipath propagation channel.
 20. Thereceiver of claim 19, wherein the equalization selector is configured toselect the frequency-domain equalizer to perform FDE on the SC if theeffective SNR of the SC after having being processed by the time-domainequalizer, using a maximum number of the programmable filter taps, isexpected to be less than the required SNR.
 21. The receiver of claim 20,wherein a power consumption associated with the time-domain equalizerusing the maximum number of the programmable filter taps is less than apower consumption associated with the frequency-domain equalizer.